Cover for air bag installation

ABSTRACT

An improved automotive air bag assembly includes a sheet metal housing having a cover formed of a homogeneous plastic. The cover is formed with locking arms for engaging the rim of the housing. Two of the locking arms are clamped onto the rim by a clamping member and two orthogonal locking arms are not so clamped. The cover defines tear lines whose thickness varies to control the sequence and direction of tear whereby doors are created whose hinges form in thickened regions of the cover material.

TECHNICAL FIELD

This invention relates to air bags for automotive crash protection Morespecifically, it relates to an improved cover assembly for an air baginstallation.

BACKGROUND ART

Automotive air bags are commonly installed to protect both the driverand the front seat passenger from injury in the event of a head-oncollision. The term "air bag" is something of a misnomer because,typically, the bag is filled with a rapidly evolving gas produced by anignitor. The bag is designed to inflate in no more than approximately 50milliseconds. In its uninflated and folded condition it is mountedwithin a housing having a cover which is designed to tear alongpredetermined lines to provide an opening for the escape of the air bag.

In view of the explosive nature of the air bag inflation, one of themajor problems with prior art installations has been the tendency of theair bag cover to part from its housing or to break into pieces. The airbag cover or its pieces thereby become projectiles capable of inflictingdamage on the occupants.

Various approaches have been employed in the prior art to overcome thisproblem. In one such approach, the plastic cover member is strengthenedby embedding therein a fabric band made of a highly tear resistantmaterial Such an approach, for example, is disclosed in U.S. Pat. No.4,334,699 of Patzelt et al. In another approach disclosed in U.S. Pat.No. 5,092,627 of Igawa, the plastic cover is riveted to a metal platewhich deforms as the cover breaks open. U.S. Pat. No. 4,968,057 ofRafferty discloses metal sheet inserts which are also riveted to thehousing. Other approaches to the solving of these problems will be foundin U.S. Pat. Nos. 4,148,503 of Shiratori et al., U.S. Pat. No. 4,852,907of Shiraki et al., and U.S. Pat. No. 5,013,065 of Kreuzer.

One of the major problems with all of the prior art solutions is thatthey are expensive to implement and result in an undesirably heavy airbag installation. Furthermore, the covers lack flexibility with theresult that they are not easily assembled. Accordingly, it is a primaryobject of the present invention to provide an air bag installationcomprising a molded cover which requires no reinforcements. Anotherobject is to provide such a cover which is sufficiently flexible that itmay be readily assembled to the air bag housing. Another object is toprovide such an assembly wherein the energy of the expanding air bag isdissipated in a managed way to prevent the cover from breaking up.Another object is to provide a cover which is designed so that, as itopens, it flexes in such a manner that it becomes more firmly secured tothe housing. Other objects, features, and advantages will becomeapparent from the following description and appended claims.

DISCLOSURE OF INVENTION

The invention comprises a sheet metal air bag housing having aperipheral rim. A molded plastic cover includes a plurality of lockingarms which engage the rim of the housing. A retainer mounted to thebottom of the housing secures a pair of opposed locking arms to thehousing rim. The cover defines tear lines in the form of an H. Thethickness of the tear lines is adjusted so that the tear begins in thecross bar of the H. As the tear progresses, the cover deforms so thatthe unretained locking arms more tightly engage the housing rim. Thetear line thickness beyond the cross bar increases to dissipate energy,but then thins again to direct the tear into a hinge region at a thickerportion of the molded cover. In this manner, the doors formed by thetearing of the cover are prevented from separating from the cover.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section illustrating the air bag assembly of theinvention mounted within an automobile steering wheel;

FIG. 2 is a front view of the assembly of the invention;

FIG. 3 is a cross-section taken substantially along the line 3--3 ofFIG. 2;

FIG. 4 is a cross-section taken substantially along the line 4--4 ofFIG. 2;

Fig. 5 is a side view, on a reduced scale, of the assembly of theinvention;

FIG. 6 is a rear view of the assembly of FIGS. 2-5; and

FIG. 7 is a rear view of another version of a cover in accordance withthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring first to FIG. 1, there is illustrated an air bag assembly 10in accordance with the present invention, mounted within an automobilesteering wheel S. The air bag assembly 10 is illustrated in detail inFIGS. 2-4. It comprises a metal housing 12 having a circular aperture 14in its base. An annular retaining ring 16 on the inside of the housing12 surrounds the aperture 14 and is connected to the mouth of an air bag18. A cup 20 is suspended beneath the aperture 14 and encloses anignitor assembly 22. As the latter does not form a part of thisinvention, it will not be further described. Mounted to the bottom ofthe housing 12 and surrounding the cup 20 is a spider 24.

As will be apparent from FIGS. 2 and 6, the housing 12 is roughlyrectangular in shape and its upper edge carries a recurved rim 26. Thecover 28 of the housing of this invention is a molded homogeneous memberin that no reinforcements are molded into it. A high pressure injectionmolding material such as a thermoplastic is preferred. An especiallypreferred material would be a terpolymer elastomer made fromethylene-propylene diene monomer such as Santoprene (a trademark ofMonsanto Company). The cover 28 includes a solid face 30 which serves toenclose the housing 12 and airbag 18. Integrally molded with the cover28 and extending rearwardly from its face 30 are four locking arms. Thefour locking arms are independently movable for ease of mounting to thehousing. In some embodiments, the locking arms are connected by flexiblesidewalls which permit such desired independent movement. One set oflocking arms 32, 34 will be seen in FIG. 4. They are on opposite sidesof the housing 12 and each includes a notch 36 for receiving the rim 26and a reentrant recess 38 as will be most apparent in FIGS. 4 and 6. Thespider 24 which is mounted on the bottom of the housing 12 includes apair of retaining clips 40, 42 which enter the recesses 38 and serve toretain the cover 28 in position. It will be noted that the spider 24also includes a pair of mounting plates 44, 46. However, as these do notform a part of this invention, they will not be further described.

A second pair of locking arms 48, 50 projects from the rear of the cover28 substantially orthogonal to the retained locking arms 32, 34. Each ofthe locking arms 48, 50 defines a notch 52 which engages the rim 26 ofthe housing 12. These locking arms 48, 50 may be further retained by thespider 24, if desired.

Particularly referring now to FIGS. 2 and 3, it will be noted that theinner surface of the cover face 30 defines an array of tear lines. Theseare thin portions of the face 30 which split when the air bag 18inflates to thereby form hinged doors 54, 56 as shown in FIG. 1. Thetear lines are generally in the form of the letter H. The thinnest 58 ofthe tear lines represents the cross bar of the H as viewed in FIG. 2.Side tear lines 60, 62 represent the sides of the H. At each end of eachside tear line 60, 62 a curved portion 64 leads into a hinge region 66,68 adjacent one of the locking arms 32, 34.

The tear lines are designed to open in a preselected sequence whichserves the multiple purposes of: (1) increasing the retention forcebetween the cover 28 and the housing 12; (2) dissipating the energy ofthe expanding air bag 18; and (3) preventing the newly formed doors 54,56 from detaching from the main body of the cover 28.

The tear lines within the region labelled "A" in FIG. 2 are thethinnest. The material underlying the lines in this region may be, forexample, 0.5 mm thick. It will be seen that this includes all of thecross bar 58 and a small portion of each of the side tear lines 60, 62adjacent the cross bar. As the bag expands, the cross bar tear line 58begins to split at its center as the face 30 begins to bulge upwardly.The top and bottom of the cover 28, as viewed in FIG. 2, are firmlyretained against the parallel edges of the housing rim 26 by theretaining clips 40, 42 of the spider 24. However, the absence of anystiffening of the cover 28 at the corners of the housing 12 causes thecover 28 to flex inwardly at its sides, thereby causing the locking arms48, 50 seen in FIG. 3 to be forced inwardly against the housing 12. Inthis manner, the cover 28 resists any tendency to separate from thehousing 12.

The cross bar tear line 58 continues to tear along its entire length andthe tear continues into the thinner regions of side tear lines 60, 62.At that point, however, the tear enters the region "B" and in thisregion the thickness of the tear lines essentially doubles to 1.1-2 mm,thereby dissipating more of the air bag energy.

At the end of each of the thicker tear line portions, it is desired tochannel the tear into a thick hinge area which includes the locking arms32, 34. This is achieved by means of a tuned tensile energy dissipationline comprising the return portion 64 at each end of side tear lines 60,62 in the region "C" shown in FIG. 3. The portions 64 tear away intension to dissipate energy from the opening door. Within this region,the tear line thickness is reduced to approximately 0.7-0.9 mm and theline is approximately perpendicular to the direction of travel of thedoors 54, 56. In this manner the tear is directed into the desired hingeregion of extra thickness at the locking arms 32, 34.

FIG. 7 illustrates a modified cover 70. Except for shape, the modifiedcover 70 closely resembles that of FIGS. 1-6 and includes, for example,retained locking arms 72, 74 and non-retained locking arms 76, 78. Thetear line array differs slightly in that the cross bar tear line 80 ismore centrally positioned within the face 82 of the cover 70. Otherwise,however, the cover 70 is quite similar to the previously described cover28.

It is believed that the many advantages of this invention will now beapparent to those skilled in the art. It will also be apparent that anumber of variations and modifications may be made therein withoutdeparting from its spirit and scope. Accordingly, the foregoingdescription is to be construed as illustrative only, rather thanlimiting. This invention is limited only by the scope of the followingclaims.

What is claimed is:
 1. In an air bag assembly for use in a motor vehicleincluding a rigid box shaped housing having a bottom and a side walldefining a substantially open top, a collapsed air bag within saidhousing, an inflator connected to inflate said air bag, and a coverclosing said housing and defining tear lines adapted to be ruptured bythe inflating air bag, the improvement which comprises:said cover beingof a substantially homogeneous material; said tearlines being thinregions of the cover material forming a generally H-shaped patternhaving at least three portions of differing thickness wherein the firstand thinnest tear line portions are the crossbar of the H and theregions of the vertical bars immediately adjacent the crossbar, thesucceeding, second portions of the vertical bars being thicker, with theend of each vertical bar terminating in a third portion defining a curveleading to a thickened hinge region of the cover, the third portionhaving a thickness intermediate that of the first and second portions;an outwardly extending rim on said side wall disposed around at least aportion of said open top; a plurality of locking arms integral with saidcover and engaging said rim; and means secured to the bottom of saidhousing for retaining at least two of said locking arms in engagementwith said rim during inflation of said air bag, whereby the thinnesttear line portions will be the first to rupture and form doors releasingsaid air bag and energy from the expanding air bag will be absorbedduring the formation of said doors.
 2. The improvement of claim 1wherein said two retained locking arms are substantially diametricallyopposed relative to said open top.
 3. The improvement of claim 2 whereinthe remaining locking arms number at least two and are substantiallydiametrically opposed relative to said open top.
 4. The improvement ofclaim 3 wherein said two retained locking arms and said two remaininglocking arms lie along substantially perpendicular axes.
 5. Theimprovement of claim 1 wherein each of said thickened cover regionsincludes one of said retained locking arms.
 6. The improvement of claim5 wherein said two retained locking arms are substantially diametricallyopposed relative to said open top.
 7. The improvement of claim 6 whereinthe remaining locking arms number at least two and are substantiallydiametrically opposed relative to said open top.
 8. The improvement ofclaim 7 wherein said top retained locking arms and said two remaininglocking arms are substantially orthogonal.
 9. A homogeneous moldedplastic cover for the open housing of an automotive air bag assemblywhich comprises:a substantially flat face portion defining thereinweakened tear lines forming a generally H-shaped pattern having at leastthree portions of differing thickness wherein the first and thinnesttear line portions are the crossbar of the H and the regions of thevertical bars immediately adjacent the crossbar, the succeeding, second,portions of the vertical bars being thicker, with the end of eachvertical bar terminating in a third portion defining a curve leading toa thickened hinge area of the cover, the third portion having athickness intermediate that of the first and second portions whereby thetear line portions rupture under the influence of an inflating air bagand doors are formed to release said air bag and absorb energy from theair bag during formation of said doors; first and second locking armsextending rearwardly from said face portion for engagement with opposedportions of a rim of said housing and adapted to be retained in saidengagement by an external retaining member; and third and fourth lockingarms extending rearwardly from said face portion and orthogonal to saidfirst and second arms for engagement with opposed portions of saidhousing rim.
 10. The cover of claim 9 wherein said plastic issufficiently resilient that, upon rupture and formation of said releasedoors, the third and fourth locking arms are forced into tighterengagement with said housing rim.
 11. The improvement of claim 9 whereineach of said thickened cover regions includes one of said first andsecond locking arms.
 12. The cover of claim 11 wherein said plastic issufficiently resiliently that, upon rupture and formation of saidrelease doors, the third and fourth locking arms are forced into tighterengagement with said housing rim.